1. Field of the Invention
The invention pertains to a corrosion inhibitor combination for cooling systems containing antifreeze with solutions based on water-soluble alcohols, and more particularly relates to such combinations containing no silicates.
2. Other Combinations in the Field
A number of other corrosion inhibitor combinations have been devised to prevent corrosion in automotive cooling systems containing antifreeze solutions based on water-soluble alcohols. For example, U.S. Pat. No. 4,242,214 to Lambert describes a combination which includes sodium tetraborate, sodium benzoate, sodium metaborate, sodium metasilicate and tolyltriazole or benzotriazole.
British Military Specification TS 10177 (March, 1978) calls for the use of 4.0 to 4.5 wt. % disodium sebacate and 0.25 to 0.30 wt. % benzotriazole as an effective corrosion inhibitor package for an antifreeze formulation. See also British Pat. No. 1,004,259 to Aiken, et al. which teaches a corrosion inhibitor composition having a mixture of benzotriazole and/or methylbenzotriazole and an alkali metal, ammonium, amine or alkanolamine salt of a saturated dicarboxylic acid having from six to thirty carbon atoms per molecule.
U.S. Patent 4,382,008 to Boreland, et al. relates to an antifreeze corrosion inhibitor composed of a triazole, an alkali metal borate, an alkali metal benzoate or homologue thereof, an alkali metal silicate and an alkali metal salt of a dibasic organic acid having 7 to 13 carbon atoms. French Certificate of Utility No. 2,489,355 to Perrot teaches sodium sebacate as a corrosion inhibitor for glycol antifreezes based on monoethylene or monopropylene glycol optionally in conjunction with other additives, especially sodium metasilicate, K.sub.2 HPO.sub.4, tolutriazole or 1,2,3-benzotriazole.
A metal corrosion inhibitor having (1) a compound selected from the group of benzoic acid, sodium benzoate and potassium benzoate, (2) a compound selected from the group of nitrous acid, sodium nitrite and potassium nitrite, (3) a compound selected from the group of phosphoric acid, sodium dihydrogenphosphate, disodium hydrogenphosphate, trisodium phosphate, potassium dihydrogenphosphate, dipotassium hydrogen-phosphate and tripotassium phosphate, and (4) a compound from the group of mercaptobenzothiazole, its salts, benzotriazole and tolyltriazole is revealed in U.S. Pat. No. 4,338,209 to Manabe, et al. Further, U.S. Pat. No. 4,455,248 to Wood discloses a single-phase glycol-based antifreeze composition having multi-metal corrosion protection which contains certain silicate, phosphate, borate, nitrate, azole and alkali compounds in specified proportions.
Silicates are excellent corrosion inhibitors, especially for aluminum components, but they suffer from two major disadvantages. First, they have a tendency to form an insoluble gel during storage. Expensive organosilanes must then be used to prevent gel formation in the antifreeze. Second, silicates have a tendency to become depleted from the solution over the life of the antifreeze. This depletion results in a reduction in the corrosion protection provided by the antifreeze.
Thus, it is an object of this invention to provide an antifreeze formulation which gives corrosion protection results as good as those obtained with silicate-based corrosion inhibition systems, but without the silicates.